Thermoplastic resin composition

ABSTRACT

Provided is a thermoplastic resin composition which includes: a first graft copolymer including a C4 to C10 alkyl (meth)acrylate-based monomer unit, a C1 to C3 alkyl-substituted styrene-based monomer unit, and a vinyl cyan-based monomer unit; a second graft copolymer including a C4 to C10 alkyl (meth)acrylate-based monomer unit, an alkyl-unsubstituted styrene-based monomer unit, and a vinyl cyan-based monomer unit; a first styrene-based copolymer including a C1 to C3 alkyl-substituted styrene-based monomer unit and a vinyl cyan-based monomer unit; a second styrene-based copolymer including an alkyl-unsubstituted styrene-based monomer unit and a vinyl cyan-based monomer unit; and an olefin-based copolymer including a C1 to C3 alkyl (meth)acrylate-based monomer unit. The thermoplastic resin composition exhibits remarkably excellent chemical resistance and remarkably excellent appearance characteristics while maintaining basic properties.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a National Phase of International Application No. PCT/KR2019/014261, which claims priority to and the benefit of Korean Patent Application No. 10-2018-0132191, filed on Oct. 31, 2018, the disclosures of which are incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a thermoplastic resin composition, specifically, a thermoplastic resin composition exhibiting excellent chemical resistance and excellent appearance characteristics.

BACKGROUND ART

Generally, an acrylic-based graft copolymer formed by graft polymerization of an acrylic-based rubber polymer with an aromatic vinyl-based monomer and a vinyl cyan-based monomer exhibits excellent weather resistance and excellent aging resistance. A thermoplastic resin composition including such an acrylic-based graft copolymer is used in various fields such as automobiles, ships, leisure products, building materials, horticultural products, and the like, and the usage thereof is rapidly increasing.

Meanwhile, with an increased need of a user for emotional quality, research to realize a classy appearance, excellent colorability, and excellent weather resistance by finishing base materials such as PVC, steel sheets, and the like with the thermoplastic resin composition has been conducted.

Since a decorative sheet including an acrylic-based graft copolymer exhibits excellent processing stability compared to conventional PVC or PP and does not include a heavy metal component, it has attracted attention as an environmentally friendly material. However, the decorative sheet has a problem in which pressure marks are left during the storage process or the dimensions of the sheet are deformed (expanded or reduced) during processing. In addition, when an adhesive is used for adhesion to the base material, the decorative sheet may be dissolved due to poor chemical resistance.

Therefore, there is a need to develop a thermoplastic resin composition exhibiting improved appearance quality and improved chemical resistance.

DISCLOSURE Technical Problem

The present invention is directed to providing a thermoplastic resin composition which exhibits improved chemical resistance, improved heat resistance, and improved appearance characteristics while being excellent in basic properties such as processability, hardness, colorability, impact resistance, and the like.

Technical Solution

One aspect of the present invention provides a thermoplastic resin composition which includes: a first graft copolymer including a C₄ to C₁₀ alkyl (meth)acrylate-based monomer unit, a C₁ to C₃ alkyl-substituted styrene-based monomer unit, and a vinyl cyan-based monomer unit; a second graft copolymer including a C₄ to C₁₀ alkyl (meth)acrylate-based monomer unit, an alkyl-unsubstituted styrene-based monomer unit, and a vinyl cyan-based monomer unit; a first styrene-based copolymer including a C₁ to C₃ alkyl-substituted styrene-based monomer unit and a vinyl cyan-based monomer unit; a second styrene-based copolymer including an alkyl-unsubstituted styrene-based monomer unit and a vinyl cyan-based monomer unit; and an olefin-based copolymer including a C₁ to C₃ alkyl (meth)acrylate-based monomer unit.

Advantageous Effects

A thermoplastic resin composition according to the present invention can exhibit significantly improved chemical resistance, heat resistance, and appearance characteristics while being excellent in basic properties such as processability, hardness, colorability, impact resistance, and the like.

Modes of the Invention

Hereinafter, the present invention will be described in more detail to facilitate understanding of the present invention.

Terms and words used in this specification and claims should not be interpreted as being limited to commonly used meanings or meanings in dictionaries, and, based on the principle that the inventors can appropriately define concepts of terms in order to describe their invention in the best way, the terms and words should be interpreted with meanings and concepts which are consistent with the technological spirit of the present invention.

In the present invention, the weight-average molecular weight of a shell of a graft copolymer may refer to a weight-average molecular weight of a copolymer including an aromatic vinyl-based monomer unit and a vinyl cyan-based monomer unit which are grafted onto a core.

Here, the aromatic vinyl-based monomer unit may be one or more selected from the group consisting of a C₁ to C₃ alkyl-substituted styrene-based monomer unit and an alkyl-unsubstituted styrene-based monomer unit.

In the present invention, the weight-average molecular weight of a shell of a graft copolymer may be measured as a relative value with respect to a standard polystyrene (PS) sample by gel permeation chromatography (GPC, Waters Breeze) after the graft copolymer is dissolved in acetone and centrifuged and the portion (sol) dissolved in acetone is then dissolved in tetrahydrofuran (THF).

In the present invention, the degree of grafting for a graft copolymer may be calculated by the following equation.

Degree of grafting (%): Weight (g) of grafted monomers/Weight (g) of rubber×100

Weight (g) of grafted monomers: Weight of insoluble substance (gel) obtained after graft copolymer powder is dissolved in acetone and centrifuged

Weight (g) of rubber: Weight of C₄ to C₁₀ alkyl (meth)acrylate-based monomer theoretically added in the preparation of graft copolymer powder

In the present invention, the average particle diameters of a seed, a core, and a graft copolymer may be measured by a dynamic light scattering method, specifically, by using a Nicomp 380 instrument (manufactured by PSS Nicomp).

In the present invention, an average particle diameter may refer to an arithmetic average particle diameter in the particle size distribution as measured by a dynamic light scattering method, specifically, an average particle diameter measured in the scattering intensity distribution.

In the present invention, a weight-average molecular weight may be measured as a relative value with respect to a standard PS sample by GPC (Waters Breeze) using THF as an eluate.

1. Thermoplastic Resin Composition

A thermoplastic resin composition according to an embodiment of the present invention includes: A-1) a first graft copolymer including a C₄ to C₁₀ alkyl (meth)acrylate-based monomer unit, a C₁ to C₃ alkyl-substituted styrene-based monomer unit, and a vinyl cyan-based monomer unit; A-2) a second graft copolymer including a C₄ to C₁₀ alkyl (meth)acrylate-based monomer unit, an alkyl-unsubstituted styrene-based monomer unit, and a vinyl cyan-based monomer unit; B-1) a first styrene-based copolymer including a C₁ to C₃ alkyl-substituted styrene-based monomer unit and a vinyl cyan-based monomer unit; B-2) a second styrene-based copolymer including an alkyl-unsubstituted styrene-based monomer unit and a vinyl cyan-based monomer unit; and C) an olefin-based copolymer including a C₁ to C₃ alkyl (meth)acrylate-based monomer unit.

Hereinafter, each component of the thermoplastic resin composition according to the present invention will be described in detail.

A-1) First Graft Copolymer

The first graft copolymer includes a C₄ to C₁₀ alkyl (meth)acrylate-based monomer unit, a C₁ to C₃ alkyl-substituted styrene-based monomer unit, and a vinyl cyan-based monomer unit.

Since the first graft copolymer includes a C₁ to C₃ alkyl-substituted styrene-based monomer unit, it may impart remarkably excellent heat resistance and remarkably excellent appearance characteristics to the thermoplastic resin composition. In addition, the first graft copolymer may be uniformly dispersed in the thermoplastic resin composition due to having significantly improved compatibility with a first styrene-based copolymer to be described below.

In addition, the first graft copolymer may impart excellent impact resistance to the thermoplastic resin composition.

The first graft copolymer may have a core-shell structure including: a core formed of a crosslinked polymer including a C₄ to C₁₀ alkyl (meth)acrylate-based monomer unit; and a shell including an alkyl-substituted styrene-based monomer unit and a vinyl cyan-based monomer unit which are grafted onto the core.

The C₄ to C₁₀ alkyl (meth)acrylate-based monomer unit may be a unit derived from a C₄ to C₁₀ alkyl (meth)acrylate-based monomer.

The C₄ to C₁₀ alkyl (meth)acrylate-based monomer may be one or more selected from the group consisting of butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, and decyl (meth)acrylate, with butyl acrylate being preferred.

The C₄ to C₁₀ alkyl (meth)acrylate-based monomer unit may be included in an amount of 40 to 60 wt % or 45 to 55 wt % with respect to the total weight of the first graft copolymer, with the range of 45 to 55 wt % being preferred. When the above-described range is satisfied, the impact resistance of the first graft copolymer can be improved.

The C₁ to C₃ alkyl-substituted styrene-based monomer unit may be a unit derived from a C₁ to C₃ alkyl-substituted styrene-based monomer.

The C₁ to C₃ alkyl-substituted styrene-based monomer may be one or more selected from the group consisting of u-methylstyrene, p-methylstyrene, and 2,4-dimethylstyrene, with u-methylstyrene being preferred.

The C₁ to C₃ alkyl-substituted styrene-based monomer unit may be included in an amount of 25 to 45 wt % or 30 to 40 wt % with respect to the total weight of the first graft copolymer, with the range of 30 to 40 wt % being preferred. When the above-described range is satisfied, the heat resistance, appearance characteristics, and impact resistance of the thermoplastic resin composition can be improved.

The vinyl cyan-based monomer unit may be a unit derived from a vinyl cyan-based monomer.

The vinyl cyan-based monomer may be one or more selected from the group consisting of acrylonitrile, methacrylonitrile, and ethacrylonitrile, with acrylonitrile being preferred.

The vinyl cyan-based monomer unit may be included in an amount of 5 to 25 wt % or 10 to 20 wt % with respect to the total weight of the first graft copolymer, with the range of 10 to 20 wt % being preferred. When the above-described range is satisfied, the chemical resistance of the first graft copolymer can be improved.

The first graft copolymer may further include an alkyl-unsubstituted styrene-based monomer unit to facilitate polymerization. The alkyl-unsubstituted styrene-based monomer unit may be a unit derived from an alkyl-unsubstituted styrene-based monomer. The alkyl-unsubstituted styrene-based monomer may be one or more selected from the group consisting of styrene, p-bromostyrene, o-bromostyrene, and p-chlorostyrene, with styrene being preferred.

The alkyl-unsubstituted styrene-based monomer unit may be included in an amount of 0.1 to 15 wt % or 1 to 10 wt % with respect to the total weight of the first graft copolymer, with the range of 1 to 10 wt % being preferred. When the above-described range is satisfied, polymerization of the first graft copolymer can more easily proceed.

The core of the first graft copolymer may have an average particle diameter different from that of the second graft copolymer, and specifically, the core of the first graft copolymer may have an average particle diameter greater than that of the second graft copolymer.

Since the thermoplastic resin composition includes at least two types of graft copolymers having cores having mutually different average particle diameters, all of impact resistance, weather resistance, colorability, surface gloss characteristics, and appearance characteristics can be improved.

The core of the first graft copolymer may have an average particle diameter of 300 to 500 nm or 350 to 450 nm, with the range of 350 to 450 nm being preferred. When the above-described range is satisfied, the impact resistance and surface gloss characteristics of the thermoplastic resin composition can be improved. Below the above-described range, the impact resistance of the thermoplastic resin composition may be degraded, and above the above-described range, the surface gloss characteristics thereof may be degraded.

The first graft copolymer may have a degree of grafting of 20 to 100%, 40 to 80%, or 45 to 60%, with the range of 40 to 60% being preferred. When the above-described range is satisfied, the impact resistance and dispersibility of the thermoplastic resin composition can be improved.

The shell of the first graft copolymer may have a weight-average molecular weight of 100,000 to 300,000 g/mol or 150,000 to 250,000 g/mol, with the range of 150,000 to 250,000 g/mol being preferred. When the above-described range is satisfied, the impact resistance of the thermoplastic resin composition can be improved.

The first graft copolymer may be selected from the group consisting of a butyl acrylate/u-methylstyrene/acrylonitrile copolymer and a butyl acrylate/styrene/u-methylstyrene/acrylonitrile copolymer, with the butyl acrylate/styrene/u-methylstyrene/acrylonitrilecopolymerbeingpreferred.

The first graft copolymer may be included in an amount of 5 to 30 parts by weight, 10 to 25 parts by weight, or 10 to 15 parts by weight with respect to 100 parts by weight of the sum of the first graft copolymer, the second graft copolymer, the first styrene-based copolymer, and the second styrene-based copolymer, with the range of 10 to 15 parts by weight being preferred. When the above-described range is satisfied, the impact resistance of the thermoplastic resin composition can be significantly improved. Below the above-described range, the impact resistance and appearance characteristics of the thermoplastic resin composition may be significantly degraded, and above the above-described range, the appearance characteristics thereof may be significantly degraded.

Meanwhile, the first graft copolymer may be prepared by a method including the steps of: 1) preparing a core by polymerizing one or more selected from the group consisting of a C₄ to C₁₀ alkyl (meth)acrylate-based monomer, a C₁ to C₃ alkyl-substituted styrene-based monomer, an alkyl-unsubstituted styrene-based monomer, and a vinyl cyan-based monomer; and 2) in the presence of the core, preparing a shell by polymerizing a C₁ to C₃ alkyl-substituted styrene-based monomer and a vinyl cyan-based monomer.

The step—of preparing a core may include the steps of: preparing a seed by polymerizing one or more selected from the group consisting of a C₄ to C₁₀ alkyl (meth)acrylate-based monomer, a C₁ to C₃ alkyl-substituted styrene-based monomer, an alkyl-unsubstituted styrene-based monomer, and a vinyl cyan-based monomer; and, in the presence of the seed, preparing a core by polymerizing a C₄ to C₁₀ alkyl (meth)acrylate-based monomer.

The preparation of a seed and a core may be performed in the presence of one or more selected from the group consisting of an emulsifier, an initiator, a crosslinking agent, a grafting agent, an electrolyte, and water.

The emulsifier may be one or more selected from the group consisting of metal salt derivatives of a C₁₂ to Cis alkyl sulfosuccinic acid and metal salt derivatives of a C₁₂ to C₂₀ alkyl sulfuric acid ester.

The metal salt derivative of a C₁₂ to Cis alkyl sulfosuccinic acid may be one or more selected from the group consisting of dicyclohexyl sodium sulfosuccinate, dihexyl sodium sulfosuccinate, di-2-ethylhexyl sodium sulfosuccinate, di-2-ethylhexyl potassium sulfosuccinate, and di-2-ethylhexyl lithium sulfosuccinate.

The metal salt derivative of a C₁₂ to C₂₀ alkyl sulfuric acid ester may be one or more selected from the group consisting of sodium dodecyl sulfate, sodium dodecylbenzenesulfate, sodium octadecyl sulfate, sodium oleic sulfate, potassium dodecyl sulfate, and potassium octadecyl sulfate.

The initiator may be an inorganic peroxide or an organic peroxide. The inorganic peroxide is a water-soluble initiator and may be one or more selected from the group consisting of potassium persulfate, sodium persulfate, and ammonium persulfate. The organic peroxide is a fat-soluble initiator and may be one or more selected from the group consisting of cumene hydroperoxide and benzoyl peroxide.

The crosslinking agent may be one or more selected from the group consisting of ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, 1,3-butanediol dimethacrylate, 1,6-hexanediol dimethacrylate, neopentyl glycol dimethacrylate, trimethylolpropane trimethacrylate, and trimethylolmethane triacrylate.

The grafting agent may be one or more selected from the group consisting of allyl methacrylate, triallyl isocyanurate, triallylamine, and diallylamine.

The electrolyte may be one or more selected from the group consisting of KCl, NaCl, KHCO₃, NaHCO₃, K₂CO₃, Na₂CO₃, KHSO₃, NaHSO₄, Na₂S₂O₇, K₄P₂O₇, K₃PO₄, Na₃PO₄ or Na₂HPO₄, KOH, and NaOH, with KOH being preferred.

The water serves as a medium in emulsion polymerization and may be ion exchanged water.

Meanwhile, in the preparation of a shell, a C₁ to C₃ alkyl-substituted styrene-based monomer and a vinyl cyan-based monomer may be polymerized while being continuously added at a predetermined rate. When the C₁ to C₃ alkyl-substituted styrene-based monomer and the vinyl cyan-based monomer are added by the above-described method, heat can be controlled and a runaway reaction caused by excessive release of heat can be easily suppressed during polymerization.

The polymerization may be emulsion polymerization and may be performed at 50 to 85° C. or 60 to 80° C., with the range of 60 to 80° C. being preferred. When the above-described range is satisfied, emulsion polymerization can be stably performed.

The preparation of a shell may be performed in the presence of one or more selected from the group consisting of an emulsifier, an initiator, and water.

It is preferable that the polymerization is performed while the emulsifier, initiator, and water are continuously added together with the styrene-based monomer and the vinyl cyan-based monomer. When the above-described condition is satisfied, a constant pH can be maintained to facilitate graft polymerization, and a graft copolymer whose particles have not only excellent stability but also a uniform internal structure can be prepared.

The emulsifier may be a metal salt derivative of a carboxylic acid, and the metal salt derivative of a carboxylic acid may be one or more selected from the group consisting of metal salts of a C₁₂ to C₂₀ fatty acid and metal salts of rosin acid.

The metal salt of a C₁₂ to C₂₀ fatty acid may be one or more selected from the group consisting of sodium salts of a fatty acid, sodium laurate, sodium oleate, and potassium oleate.

The metal salt of rosin acid may be one or more selected from the group consisting of sodium rosinate and potassium rosinate.

Types of the initiator have been described above, with the organic peroxide being preferred, and t-butylperoxy ethylhexyl carbonate being more preferred.

Meanwhile, the graft copolymer prepared by the above-described method may be a latex form.

The graft copolymer in latex form may be subjected to coagulation, aging, washing, dehydration, and drying to form a graft copolymer in powder form.

A-2) Second Graft Copolymer

The second graft copolymer includes a C₄ to C₁₀ alkyl (meth)acrylate-based monomer unit, an alkyl-unsubstituted styrene-based monomer unit, and a vinyl cyan-based monomer unit.

The second graft copolymer may impart excellent weather resistance, colorability, impact resistance, chemical resistance, and surface gloss characteristics to the thermoplastic resin composition.

In addition, since the second graft copolymer includes an alkyl-unsubstituted styrene-based monomer unit, it may be uniformly dispersed in the thermoplastic resin composition due to having significantly improved compatibility with a second styrene-based copolymer to be described below.

The second graft copolymer may have a core-shell structure including: a core formed of a crosslinked polymer including one or more selected from the group consisting of a C₄ to C₁₀ alkyl (meth)acrylate-based monomer unit, an alkyl-unsubstituted styrene-based monomer unit, and a vinyl cyan-based monomer unit; and a shell including an alkyl-unsubstituted styrene-based monomer unit and a vinyl cyan-based monomer unit which are grafted onto the core.

The C₄ to C₁₀ alkyl (meth)acrylate-based monomer unit may be included in an amount of 40 to 60 wt % or 45 to 55 wt % with respect to the total weight of the second graft copolymer, with the range of 45 to 55 wt % being preferred. When the above-described range is satisfied, the weather resistance and impact resistance of the second graft copolymer can be improved.

The alkyl-unsubstituted styrene-based monomer unit may be included in an amount of 25 to 45 wt % or 30 to 40 wt % with respect to the total weight of the second graft copolymer, with the range of 30 to 40 wt % being preferred. When the above-described range is satisfied, the processability and impact resistance of the second graft copolymer can be improved.

The vinyl cyan-based monomer unit may be included in an amount of 5 to 25 wt % or 10 to 20 wt % with respect to the total weight of the second graft copolymer, with the range of 10 to 20 wt % being preferred. When the above-described range is satisfied, the chemical resistance of the second graft copolymer can be improved.

The descriptions of the C₄ to C₁₀ alkyl-unsubstituted styrene-based monomer unit, the alkyl-unsubstituted styrene-based monomer unit, and the vinyl cyan-based monomer unit have been described above.

The core of the second graft copolymer may have an average particle diameter of 50 to 150 nm or 75 to 125 nm, with the range of 75 to 125 nm being preferred. When the above-described range is satisfied, the specific surface area of the core in the thermoplastic resin composition is increased to significantly improve weather resistance, and visible light can penetrate without being scattered in the core to significantly improve colorability. In addition, the chemical resistance, appearance characteristics, and surface gloss characteristics of the thermoplastic resin composition can be improved. Below the above-described range, the weather resistance, chemical resistance, appearance characteristics, and surface gloss characteristics of the thermoplastic resin composition may be significantly degraded, and above the above-described range, the weather resistance and colorability thereof may be significantly degraded.

The second graft copolymer may have a degree of grafting of 20 to 80% or 25 to 60%, with the range of 25 to 60% being preferred. When the above-described range is satisfied, a second graft copolymer exhibiting excellent colorability, excellent dispersibility, and excellent surface gloss characteristics can be prepared.

The shell of the second graft copolymer may have a weight-average molecular weight of 50,000 to 200,000 g/mol or 70,000 to 170,000 g/mol, with the range of 70,000 to 170,000 g/mol being preferred. When the above-described range is satisfied, a second graft copolymer exhibiting excellent dispersibility and excellent mechanical properties can be prepared.

The second graft copolymer may be a butyl acrylate/styrene/acrylonitrile copolymer.

The second graft copolymer may be included in an amount of 0.1 to 15 parts by weight, 1 to 10 parts by weight, or 5 to 8 parts by weight with respect to 100 parts by weight of the sum of the first graft copolymer, the second graft copolymer, the first styrene-based copolymer, and the second styrene-based copolymer, with the range of 5 to 8 parts by weight being preferred. When the above-described range is satisfied, the weather resistance, chemical resistance, colorability, appearance characteristics, and surface gloss characteristics of the thermoplastic resin composition can be significantly improved. Below the above-described range, the appearance characteristics, weather resistance, and colorability of the thermoplastic resin composition may be degraded, and above the above-described range, the impact resistance of the thermoplastic resin composition may be degraded.

Meanwhile, the second graft copolymer may be prepared by a method including the steps of: 1) preparing a core by polymerizing one or more selected from the group consisting of a C₄ to C₁₀ alkyl (meth)acrylate-based monomer, an alkyl-unsubstituted styrene-based monomer, and a vinyl cyan-based monomer; and 2) in the presence of the core, preparing a shell by polymerizing an alkyl-unsubstituted styrene-based monomer and a vinyl cyan-based monomer.

The step of preparing a core may include the steps of: preparing a seed by polymerizing one or more selected from the group consisting of a C₄ to C₁₀ alkyl (meth)acrylate-based monomer, an alkyl-unsubstituted styrene-based monomer, and a vinyl cyan-based monomer; and, in the presence of the seed, preparing a core by polymerizing a C₄ to C₁₀ alkyl (meth)acrylate-based monomer.

Other descriptions of the preparation method of the second graft copolymer have been given in the preparation method of the first graft copolymer.

Meanwhile, in the present invention, the sum of the content of the first graft copolymer and the content of the second graft copolymer may be 10 to 35 parts by weight, preferably, 15 to 30 parts by weight with respect to 100 parts by weight of the sum of the first graft copolymer, the second graft copolymer, the first styrene-based copolymer, and the second styrene-based copolymer. When the above-described range is satisfied, the thermoplastic resin composition can attain excellent impact resistance, excellent appearance characteristics, and excellent hardness. Below the above-described range, the impact resistance of the thermoplastic resin composition may be significantly degraded, and above the above-described range, a melt flow index may be lowered, and appearance characteristics may be significantly degraded.

In addition, in the present invention, a weight ratio of the first graft copolymer and the second graft copolymer may be 1.5:1 to 10:1, preferably 1.5:1 to 5:1, and more preferably 1.5:1 to 3:1. When the above-described range is satisfied, the impact resistance and appearance characteristics of the thermoplastic resin composition can be improved. Below the above-described range, the impact resistance of the thermoplastic resin composition may be degraded, and above the above-described range, the appearance characteristics of the thermoplastic resin composition may be degraded.

B-1) First Styrene-Based Copolymer

The first styrene-based copolymer is a matrix copolymer and includes a C₁ to C₃ alkyl-substituted styrene-based monomer unit and a vinyl cyan-based monomer unit.

The first styrene-based copolymer may impart excellent heat resistance and excellent appearance characteristics to the thermoplastic resin composition. Specifically, excellent heat resistance can provide improved dimensional stability of a molded article formed of the thermoplastic resin composition and minimized pressure marks.

In addition, since the first styrene-based copolymer includes a C₁ to C₃ alkyl-substituted styrene-based monomer unit, it may be highly compatible with the first graft copolymer.

Types of the C₁ to C₃ alkyl-substituted styrene-based monomer unit and the vinyl cyan-based monomer unit have been described above.

The first styrene-based copolymer may be a copolymer of a monomer mixture including a C₁ to C₃ alkyl-substituted styrene-based monomer and a vinyl cyan-based monomer.

The monomer mixture may include a C₁ to C₃ alkyl-substituted styrene-based monomer and a vinyl cyan-based monomer in a weight ratio of 60:40 to 90:10 or 65:35 to 85:15, with the range of 65:35 to 85:15 being preferred. When the above-described range is satisfied, heat resistance can be improved.

The first styrene-based copolymer may further include an alkyl-unsubstituted styrene-based monomer unit to facilitate polymerization.

That is, the first styrene-based copolymer may be a copolymer of a monomer mixture including a C₁ to C₃ alkyl-substituted styrene-based monomer, a vinyl cyan-based monomer, and an alkyl-unsubstituted styrene-based monomer. Types of the alkyl-unsubstituted styrene-based monomer unit have been described above.

In this case, the monomer mixture may include the C₁ to C₃ alkyl-substituted styrene-based monomer at 55 to 75 wt %, the vinyl cyan-based monomer at 20 to 40 wt %, and the alkyl-unsubstituted styrene-based monomer at 0.1 to 15 wt %, and preferably includes the C₁ to C₃ alkyl-substituted styrene-based monomer at 60 to 70 wt %, the vinyl cyan-based monomer at 25 to 35 wt %, and the alkyl-unsubstituted styrene-based monomer at 1 to 10 wt %. When the above-described range is satisfied, polymerization of the first styrene-based copolymer can more easily proceed.

The first styrene-based copolymer may have a weight-average molecular weight of 50,000 to 150,000 g/mol or 70,000 to 130,000 g/mol, with the range of 70,000 to 130,000 g/mol being preferred. When the above-described range is satisfied, excellent chemical resistance and mechanical properties can be realized. Below the above-described range, the mechanical properties of the thermoplastic resin composition may be degraded. Above the above-described range, processability may be degraded.

The first styrene-based copolymer may be selected from the group consisting of an α-methylstyrene/acrylonitrile copolymer and an α-methylstyrene/styrene/acrylonitrile copolymer, with the α-methylstyrene/acrylonitrile copolymer being preferred.

The first styrene-based copolymer may be included in an amount of 2 to 25 parts by weight, 7 to 20 parts by weight, 14 to 20 parts by weight, or 14 to 16 parts by weight with respect to 100 parts by weight of the sum of the first graft copolymer, the second graft copolymer, the first styrene-based copolymer, and the second styrene-based copolymer, with the range of 14 to 16 parts by weight being preferred. When the above-described range is satisfied, the heat resistance, processability, and appearance characteristics of the thermoplastic resin composition can be improved. Specifically, below the above-described range, the heat resistance of the thermoplastic resin composition is degraded, and thus appearance characteristics may be degraded. Above the above-described range, processability and chemical resistance may be degraded.

The first styrene-based copolymer may be a copolymer prepared by suspension polymerization or bulk polymerization of a monomer mixture including a C₁ to C₃ alkyl-substituted styrene-based monomer and a vinyl cyan-based monomer, with the copolymer prepared by bulk polymerization capable of preparing a high-purity polymer being preferred.

B-2) Second Styrene-Based Copolymer

The second styrene-based copolymer is a matrix copolymer and includes an alkyl-unsubstituted styrene-based monomer unit and a vinyl cyan-based monomer unit.

The second styrene-based copolymer may impart excellent processability, chemical resistance, and mechanical properties to the thermoplastic resin composition. Since the second styrene-based copolymer includes an alkyl-unsubstituted styrene-based monomer unit, it may have improved compatibility with the second graft copolymer and thus may allow the second graft copolymer to be uniformly dispersed in the thermoplastic resin composition.

Types of the alkyl-unsubstituted styrene-based monomer unit and the vinyl cyan-based monomer unit have been described above.

The second styrene-based copolymer may be a copolymer of a monomer mixture including an alkyl-unsubstituted styrene-based monomer and a vinyl cyan-based monomer.

The monomer mixture may include an alkyl-unsubstituted styrene-based monomer and a vinyl cyan-based monomer in a weight ratio of 60:40 to 90:10 or 65:35 to 85:15, with the range of 65:35 to 85:15 being preferred. When the above-described range is satisfied, processability and chemical resistance can be improved.

The second styrene-based copolymer may have a weight-average molecular weight of 100,000 to 250,000 g/mol or 130,000 to 220,000 g/mol, with the range of 130,000 to 220,000 g/mol being preferred. When the above-described range is satisfied, excellent chemical resistance and excellent mechanical properties can be realized. Below the above-described range, the mechanical properties of the thermoplastic resin composition may be degraded, and above the above-described range, the processability of the thermoplastic resin composition may be degraded.

It is preferable that the second styrene-based copolymer is a styrene/acrylonitrile copolymer.

The second styrene-based copolymer may be included in an amount of 50 to 80 parts by weight, 55 to 75 parts by weight, or 62 to 66 parts by weight with respect to 100 parts by weight of the sum of the first graft copolymer, the second graft copolymer, the first styrene-based copolymer, and the second styrene-based copolymer, with the range of 62 to 66 parts by weight being preferred. When the above-described range is satisfied, the processability, chemical resistance, and mechanical properties of the thermoplastic resin composition can be improved. Below the above-described range, the chemical resistance and processability of the thermoplastic resin composition may be degraded, and above the above-described range, the mechanical properties of the thermoplastic resin composition may be degraded.

The second styrene-based copolymer may be a copolymer prepared by suspension polymerization or bulk polymerization of an alkyl-unsubstituted styrene-based monomer and a vinyl cyan-based monomer, with the copolymer prepared by bulk polymerization capable of preparing a high-purity copolymer being preferred.

Meanwhile, in the present invention, the sum of the content of the first styrene-based copolymer and the content of the second styrene-based copolymer may be 65 to 90 parts by weight, preferably, 70 to 85 parts by weight with respect to 100 parts by weight of the sum of the first graft copolymer, the second graft copolymer, the first styrene-based copolymer, and the second styrene-based copolymer. Below the above-described range, the processability of the thermoplastic resin composition may be degraded, and above the above-described range, the impact resistance of the thermoplastic resin composition may be degraded.

C) Olefin-Based Copolymer

The olefin-based copolymer is an additive and includes a C₁ to C₃ alkyl (meth)acrylate-based monomer unit.

The olefin-based copolymer may impart excellent chemical resistance to the thermoplastic resin composition.

The olefin-based copolymer may be a copolymer of a monomer mixture including a C₂ to C₄ olefin-based monomer and a C₁ to C₃ alkyl (meth)acrylate-based monomer.

The C₂ to C₄ olefin-based monomer may be one or more selected from the group consisting of ethylene, propylene, and butene, with ethylene being preferred.

The C₁ to C₃ alkyl (meth)acrylate-based monomer may be one or more selected from the group consisting of methyl (meth)acrylate, ethyl (meth)acrylate, and propyl (meth)acrylate, with methyl acrylate being preferred.

The olefin-based copolymer may include a C₂ to C₄ olefin-based monomer unit and a C₁ to C₃ alkyl (meth)acrylate-based monomer unit in a weight ratio of 85:15 to 65:35 or 80:20 to 70:30, with the range of 80:20 to 70:30 being preferred. When the above-described range is satisfied, the chemical resistance of the olefin-based copolymer can be improved. Specifically, when the alkyl (meth)acrylate-based monomer unit is insufficiently included, the compatibility of the olefin-based copolymer with the first graft copolymer, the second graft copolymer, the first styrene-based copolymer, and the second styrene-based copolymer is degraded such that it may not be uniformly dispersed in the thermoplastic resin composition, and thus an effect of improving chemical resistance may be degraded. When the alkyl (meth)acrylate-based monomer unit is excessively included, the compatibility of the olefin-based copolymer with the first graft copolymer, the second graft copolymer, the first styrene-based copolymer, and the second styrene-based copolymer is improved, but the content of an olefin-based monomer unit is decreased, and thus an effect of improving chemical resistance may be degraded.

The olefin-based copolymer may have a weight-average molecular weight of 50,000 to 200,000 g/mol, 70,000 to 150,000 g/mol, or 90,000 to 120,000 g/mol, with the range of 90,000 to 120,000 g/mol being preferred. When the above-described range is satisfied, the olefin-based copolymer exhibits excellent compatibility with the first graft copolymer, the second graft copolymer, the first styrene-based copolymer, and the second styrene-based copolymer, and a thermoplastic resin composition exhibiting excellent mechanical properties can be provided. Specifically, below the above-described range, mechanical properties may be degraded, and above the above-described range, the compatibility of the olefin-based copolymer with the first graft copolymer, the second graft copolymer, the first styrene-based copolymer, and the second styrene-based copolymer is degraded such that it may not be uniformly dispersed in the thermoplastic resin composition, and thus an effect of improving chemical resistance may be degraded.

It is preferable that the olefin-based copolymer is an ethylene/methyl acrylate copolymer.

The olefin-based copolymer may be included in an amount of 0.01 to 2 parts by weight or 0.5 to 1 part by weight with respect to 100 parts by weight of the sum of the first graft copolymer, the second graft copolymer, the first styrene-based copolymer, and the second styrene-based copolymer in the thermoplastic resin composition, with the range of 0.5 to 1 part by weight being preferred. When the above-described range is satisfied, the chemical resistance of the thermoplastic resin composition can be improved without adversely affecting the hardness, mechanical properties, and heat resistance thereof. Below the above-described range, the chemical resistance of the thermoplastic resin composition may be degraded, and above the above-described range, the impact resistance of the thermoplastic resin composition may be degraded.

The olefin-based polymer may be a commercially available product or directly prepared.

When the olefin-based polymer is directed prepared, one or more polymerization methods selected from the group consisting of solution polymerization, slurry polymerization, gas-phase polymerization, and high-pressure polymerization may be used.

Meanwhile, the thermoplastic resin composition according to an embodiment of the present invention may further include one or more additives selected from the group consisting of an anti-dripping agent, a flame retardant, an antibacterial agent, an antistatic agent, a stabilizer, a releasing agent, a thermal stabilizer, an UV stabilizer, an inorganic additive, a lubricant, an antioxidant, a photostabilizer, a pigment, a dye, and an inorganic filler.

It is preferable that the thermoplastic resin composition according to an embodiment of the present invention includes one or more selected from the group consisting of a lubricant, an antioxidant, and an UV stabilizer.

2. Thermoplastic Resin Molded Article

A thermoplastic resin molded article according to another embodiment of the present invention is formed of the thermoplastic resin composition according to an embodiment of the present invention and may have a heat deflection temperature of 87° C. or more and an impact strength of 6.5 kg cm/cm or more. It is preferable that the thermoplastic resin molded article has a heat deflection temperature of 89° C. or more and an impact strength of 6.7 kg cm/cm or more.

When the above-described condition is satisfied, a thermoplastic resin molded article exhibiting excellent appearance characteristics, excellent heat resistance, and excellent impact resistance can be formed.

The thermoplastic resin molded article according to another embodiment of the present invention may be a sheet, preferably, a decorative sheet for furniture.

Hereinafter, exemplary embodiments of the present invention will be described in detail so that those of ordinary skill in the art can easily carry out the present invention. However, it should be understood that the present invention can be implemented in various forms, and that the exemplary embodiments are not intended to limit the present invention thereto.

Preparation Example 1

<Preparation of Seed>

3 parts by weight of styrene, 3 parts by weight of acrylonitrile, 0.1 part by weight of sodium dodecyl sulfate as an emulsifier, 0.03 part by weight of ethylene glycol dimethacrylate as a crosslinking agent, 0.02 part by weight of allyl methacrylate as a grafting agent, 0.025 part by weight of KOH as an electrolyte, and 53.32 parts by weight of distilled water were batch-added to a nitrogen-substituted reactor, and the temperature inside the reactor was raised to 70° C. Afterward, 0.03 part by weight of potassium persulfate as an initiator was batch-added to initiate polymerization, and the polymerization was performed for 2 hours and then terminated, thereby obtaining a seed (average particle diameter: 200 nm).

The average particle diameter of the seed was measured using a Nicomp 380 instrument (manufactured by PSS Nicomp) by a dynamic light scattering method.

<Preparation of Core>

Polymerization was performed for 4 hours while continuously adding, to the seed-containing reactor, a mixture including 50 parts by weight of butyl acrylate, 0.6 part by weight of sodium dodecyl sulfate as an emulsifier, 0.1 part by weight of ethylene glycol dimethacrylate as a crosslinking agent, 0.04 part by weight of allyl methacrylate as a grafting agent, 30 parts by weight of distilled water, and 0.05 part by weight of potassium persulfate as an initiator at 70° C. and a predetermined rate. After the continuous addition was terminated, polymerization was further performed for another 1 hour and then terminated, thereby obtaining a core (average particle diameter: 400 nm).

The average particle diameter of the core was measured using a Nicomp 380 instrument (manufactured by PSS Nicomp) by a dynamic light scattering method.

<Preparation of Shell>

Polymerization was performed for 3 hours while adding, to the core-containing reactor, 35 parts by weight of u-methylstyrene, 9 parts by weight of acrylonitrile, and 39 parts by weight of distilled water and continuously adding each of a first mixture including 1.9 parts by weight of potassium rosinate as an emulsifier and 0.19 part by weight of t-butylperoxy ethylhexyl carbonate as an initiator and a second mixture including 0.16 part by weight of sodium pyrophosphate, 0.24 part by weight of dextrose, and 0.004 part by weight of ferrous sulfate as activators at 75° C. and a predetermined rate. After the continuous addition was completed, polymerization was further performed at 75° C. for another 1 hour and then terminated by lowering the temperature inside the reactor to 60° C., thereby preparing a graft copolymer latex (average particle diameter: 500 nm) including a shell.

The average particle diameter of the graft copolymer latex was measured using a Nicomp 380 instrument (manufactured by PSS Nicomp) by a dynamic light scattering method.

<Preparation of Graft Copolymer Powder>

The graft copolymer latex was coagulated at 70° C. and atmospheric pressure for 7 minutes by applying 0.8 part by weight of an aqueous calcium chloride solution (concentration: 23 wt %) thereto, aged at 93° C. for 7 minutes, dehydrated, washed, and then dried with 90° C. hot air for 30 minutes, thereby preparing a graft copolymer powder.

Preparation Example 2

<Preparation of Seed>

6 parts by weight of butylacrylate, 0.5 part by weight of sodium dodecyl sulfate as an emulsifier, 0.03 part by weight of ethylene glycol dimethacrylate as a crosslinking agent, 0.02 part by weight of allyl methacrylate as a grafting agent, 0.025 part by weight of KOH as an electrolyte, and 53.32 parts by weight of distilled water were batch-added to a nitrogen-substituted reactor, and the temperature inside the reactor was raised to 70° C. Afterward, 0.03 part by weight of potassium persulfate as an initiator was batch-added to initiate polymerization, and the polymerization was performed for 2 hours and then terminated, thereby obtaining a seed (average particle diameter: 54 nm).

The average particle diameter of the seed was measured using a Nicomp 380 instrument (manufactured by PSS Nicomp) by a dynamic light scattering method.

<Preparation of Core>

Polymerization was performed for 2.5 hours while continuously adding, to the seed-containing reactor, a mixture including 43 parts by weight of butyl acrylate, 0.5 part by weight of sodium dodecyl sulfate as an emulsifier, 0.1 part by weight of ethylene glycol dimethacrylate as a crosslinking agent, 0.1 part by weight of allyl methacrylate as a grafting agent, 30 parts by weight of distilled water, and 0.05 part by weight of potassium persulfate as an initiator at 70° C. and a predetermined rate. After the continuous addition was terminated, polymerization was further performed for another 1 hour and then terminated, thereby obtaining a core (average particle diameter: 101 nm).

The average particle diameter of the core was measured using a Nicomp 380 instrument (manufactured by PSS Nicomp) by a dynamic light scattering method.

<Preparation of Shell>

Polymerization was performed for 2.5 hours while adding, to the core-containing reactor, 36 parts by weight of styrene, 15 parts by weight of acrylonitrile, and 39 parts by weight of distilled water and continuously adding each of a first mixture including 1.5 parts by weight of potassium rosinate as an emulsifier, 0.1 part by weight of t-dodecyl mercaptan as a molecular weight controlling agent, and 0.04 part by weight of t-butylperoxy ethylhexyl carbonate as an initiator and a second mixture including 0.1 part by weight of sodium pyrophosphate, 0.12 part by weight of dextrose, and 0.002 part by weight of ferrous sulfate as activators at 75° C. and a predetermined rate. After the continuous addition was completed, polymerization was further performed at 75° C. for another 1 hour and then terminated by lowering the temperature inside the reactor to 60° C., thereby preparing a graft copolymer latex (average particle diameter: 130 nm) including a shell.

The average particle diameter of the graft copolymer latex was measured using a Nicomp 380 instrument (manufactured by PSS Nicomp) by a dynamic light scattering method.

<Preparation of Graft Copolymer Powder>

A graft copolymer powder was prepared in the same manner as in Preparation Example 1.

Preparation Example 3

A 125-ml high-pressure reactor was evacuated and then filled with nitrogen, and 30 ml of toluene was added thereto. Afterward, the reactor was placed in an appropriate thermostat, 31 mmol of aluminum (III) chloride and then 31 mmol (about 2.67 g) of methyl acrylate were added to the reactor, and the reactor was maintained for 30 minutes until the reaction temperature was stabilized. Afterward, 0.0031 mmol of azobisisobutyronitrile (AIBN) in a dissolved state in 5 ml of chlorobenzene was injected into the reactor. Subsequently, polymerization was performed for 20 hours by filling the reactor with ethylene at 35 bar and raising the reaction temperature to 70° C. After the polymerization was completed, the reaction temperature was lowered to room temperature, and ethanol (non-solvent) was then added to precipitate the prepared copolymer in a solid phase. The solid-phase copolymer was allowed to settle to remove a supernatant, and the resulting solid-phase copolymer was washed by adding ethanol again and then allowed to settle to remove a supernatant. To solidify particles in the remaining solid phase copolymer, water was added thereto, and stirring and filtration were then performed, thereby collecting only a copolymer. The copolymer thus obtained was dried in a vacuum oven at 60° C. for a day.

Meanwhile, the obtained copolymer had a weight-average molecular weight of 104,000 g/mol and included a methyl acrylate unit at 24 wt % and an ethylene unit at 76 wt %.

The weight-average molecular weight of the obtained copolymer was measured as a relative value with respect to a standard PS sample by gel permeation chromatography (GPC, Waters Breeze) using tetrahydrofuran (THF) as an eluate.

EXAMPLES AND COMPARATIVE EXAMPLES

The specifications of components used in Examples and Comparative Examples are as follows.

(A-1) First graft copolymer: The graft copolymer powder prepared in Preparation Example 1 was used.

(A-2) Second graft copolymer: The graft copolymer powder prepared in Preparation Example 2 was used.

(B-1) First styrene-based copolymer: 98UHM (commercially available from LG Chem Ltd., α-methylstyrene/acrylonitrile copolymer, weight-average molecular weight: 100,000 g/mol) was used.

The weight-average molecular weight was measured as a relative value with respect to a standard PS sample by GPC (Waters Breeze) using THF as an eluate.

(B-2) Second styrene-based copolymer: 97HC (commercially available from LG Chem Ltd., styrene/acrylonitrile copolymer, weight-average molecular weight: 170,000 g/mol) was used.

The weight-average molecular weight was measured as a relative value with respect to a standard PS sample by GPC (Waters Breeze) using THF as an eluate.

(C) Olefin-based copolymer: The copolymer prepared in Preparation Example 3 was used.

The above-described components were mixed in contents shown in the following [Table 1] and stirred to prepare thermoplastic resin compositions.

Experimental Example 1

Each of the thermoplastic resin compositions of Examples and Comparative Examples was put into a twin-screw extruder kneader set at 230° C. to prepare pellets. A physical property of the pellet was evaluated by the method described below, and results thereof are shown in the following [Table 1].

(1) Melt flow index (g/10 min): measured in accordance with ASTM D1238 at 220° C.

Experimental Example 2

The pellet prepared in Experimental Example 1 was injection-molded to prepare a specimen. Physical properties of the specimen were evaluated by methods described below, and results thereof are shown in the following [Table 1].

(2) Hardness: measured in accordance with ASTM 785.

(3) IZOD impact strength (kg cm/cm): measured in accordance with ASTM 256.

(4) Heat deflection temperature (° C.): measured in accordance with ASTM D648.

Experimental Example 3

The pellet prepared in Experimental Example 1 was extruded through a film extruder to form a 0.3-mm film. Physical properties of the film were evaluated by methods described below, and results thereof are shown in the following [Table 1].

(5) Film appearance: determined by evaluating pressure marks and bumps on the film through visual inspection.

x: deformed film, ∘: good, ⊚: excellent

(6) Chemical resistance: evaluated based on the time required for the film to start dissolving after the film was immersed in a beaker containing methyl ethyl ketone for 2 minutes.

x: 20 seconds or less, ∘: more than 40 seconds and less than 100 seconds, and ⊚: 100 seconds or more

TABLE 1 Examples Comparative Examples Classification 1 2 3 4 5 1 2 3 4 5 (A-1) First 14 19 15 14 17 3 14 14 — 22 graft copolymer (parts by weight) (A-2) Second 7 2 6 7 4 35 7 7 23 — graft copolymer (parts by weight) (B-1) First 15 12 12 15 12 — 79 15 15 15 styrene-based copolymer (B-2) Second 64 67 67 64 67 62 — 64 62 63 styrene-based copolymer (C) Olefin- 0.5 0.5 0.5 0.7 0.5 0.5 0.5 — 0.5 0.5 based copolymer Melt flow index 10.1 12.4 13 10.3 12.7 7.7 9.9 9 15.8 8.7 Hardness 112.6 112 112.3 112 112.1 104 111.9 114 113 112 Impact strength 7.1 7.1 6.7 6.6 6.9 6 7.9 7.7 4.4 7 Heat deflection 91.3 89.3 89.4 90 89.3 85 98.5 91.5 90.5 90 temperature Film appearance ⊚ ◯ ◯ ⊚ ◯ X ⊚ ⊚ X X characteristics Chemical ⊚ ⊚ ⊚ ⊚ ⊚ ◯ X X ⊚ X resistance

Referring to Table 1, it can be seen that Example 1 to Example 5 were excellent in terms of a melt flow index, hardness, impact strength, film appearance characteristics, and chemical resistance and also exhibited high heat deflection temperatures.

On the other hand, it can be seen that Comparative Example 1 not including a first styrene-based copolymer exhibited significantly degraded properties in terms of a melt flow index, heat deflection temperature, and impact strength compared to Examples and also exhibited poor film appearance characteristics.

It can be seen that Comparative Example 2 not including a second styrene-based copolymer and Comparative Example 3 not including a third copolymer exhibited significantly degraded properties in terms of a melt flow index and chemical resistance.

It can be seen that Comparative Example 4 not including a first graft copolymer exhibited significantly degraded impact strength and also exhibited poor film appearance characteristics.

It can be seen that Comparative Example 5 not including a second graft copolymer exhibited poor chemical resistance and poor film appearance characteristics.

It can be predicted from these results that only when all of the components according to the present invention are included, a thermoplastic resin molded article excellent in all of processability, hardness, impact resistance, heat resistance, chemical resistance, and appearance characteristics can be prepared. 

1. A thermoplastic resin composition comprising: a first graft copolymer including a C₄ to C₁₀ alkyl (meth)acrylate-based monomer unit, a C₁ to C₃ alkyl-substituted styrene-based monomer unit, and a vinyl cyan-based monomer unit; a second graft copolymer including a C₄ to C₁₀ alkyl (meth)acrylate-based monomer unit, an alkyl-unsubstituted styrene-based monomer unit, and a vinyl cyan-based monomer unit; a first styrene-based copolymer including a C₁ to C₃ alkyl-substituted styrene-based monomer unit and a vinyl cyan-based monomer unit; a second styrene-based copolymer including an alkyl-unsubstituted styrene-based monomer unit and a vinyl cyan-based monomer unit; and an olefin-based copolymer including a C₁ to C₃ alkyl (meth)acrylate-based monomer unit.
 2. The thermoplastic resin composition of claim 1, wherein the first graft copolymer further includes an alkyl-unsubstituted styrene-based monomer unit.
 3. The thermoplastic resin composition of claim 1, wherein the first graft copolymer and the second graft copolymer have cores having mutually different average particle diameters.
 4. The thermoplastic resin composition of claim 1, wherein the first graft copolymer has a core having an average particle diameter of 300 to 500 nm.
 5. The thermoplastic resin composition of claim 1, wherein the second graft copolymer has a core having an average particle diameter of 50 to 150 nm.
 6. The thermoplastic resin composition of claim 1, wherein the olefin-based copolymer includes a C₂ to C₄ olefin-based monomer unit and the C₁ to C₃ alkyl (meth)acrylate-based monomer unit in a weight ratio of 85:15 to 65:35.
 7. The thermoplastic resin composition of claim 1, wherein the olefin-based copolymer has a weight-average molecular weight of 50,000 to 200,000 g/mol.
 8. The thermoplastic resin composition of claim 1, which includes, with respect to 100 parts by weight of the sum of the first graft copolymer, the second graft copolymer, the first styrene-based copolymer, and the second styrene-based copolymer, 0.01 to 2 parts by weight of the olefin-based copolymer.
 9. The thermoplastic resin composition of claim 1, which includes, with respect to 100 parts by weight of the sum of the first graft copolymer, the second graft copolymer, the first styrene-based copolymer, and the second styrene-based copolymer, 0.5 to 1 part by weight of the olefin-based copolymer.
 10. The thermoplastic resin composition of claim 1, wherein the sum of the content of the first graft copolymer and the content of the second graft copolymer is 10 to 35 parts by weight with respect to 100 parts by weight of the sum of the first graft copolymer, the second graft copolymer, the first styrene-based copolymer, and the second styrene-based copolymer.
 11. The thermoplastic resin composition of claim 10, wherein a weight ratio of the first graft copolymer and the second graft copolymer is 1.5:1 to 10:1.
 12. The thermoplastic resin composition of claim 1, wherein the sum of the content of the first styrene-based copolymer and the content of the second styrene-based copolymer is 65 to 90 parts by weight with respect to 100 parts by weight of the sum of the first graft copolymer, the second graft copolymer, the first styrene-based copolymer, and the second styrene-based copolymer.
 13. The thermoplastic resin composition of claim 12, wherein the first styrene-based copolymer is included in an amount of 14 to 20 parts by weight with respect to 100 parts by weight of the sum of the first graft copolymer, the second graft copolymer, the first styrene-based copolymer, and the second styrene-based copolymer.
 14. The thermoplastic resin composition of claim 1, which includes, with respect to 100 parts by weight of the sum of the first graft copolymer, the second graft copolymer, the first styrene-based copolymer, and the second styrene-based copolymer: 5 to 30 parts by weight of the first graft copolymer; 0.1 to 15 parts by weight of the second graft copolymer; 2 to 25 parts by weight of the first styrene-based copolymer; and 50 to 80 parts by weight of the second styrene-based copolymer.
 15. The thermoplastic resin composition of claim 1, which includes, with respect to 100 parts by weight of the sum of the first graft copolymer, the second graft copolymer, the first styrene-based copolymer, and the second styrene-based copolymer: 10 to 15 parts by weight of the first graft copolymer; 5 to 8 parts by weight of the second graft copolymer; 14 to 16 parts by weight of the first styrene-based copolymer; 62 to 66 parts by weight of the second styrene-based copolymer; and 0.3 to 0.6 part by weight of the olefin-based copolymer. 